Conventionally, a wind tunnel experiment is conducted to measure forces and moments generated in an airplane model by applying a wind pressure to the airplane model. In this case, the airplane model is attached with a wind tunnel balance for measuring the forces and the moments. In general, the wind tunnel balance is provided with a plurality of strain gauges. These strain gauges detect a relationship between external forces applied actually to the airplane model and the resulting forces or moments in the wind tunnel experiment.
However, a strain (hereinafter referred to as “interference strain”) occurs in a direction different from the direction in which the external force is applied actually to the airplane model, and this is detected by the strain gauge. Therefore, in the wind tunnel balance, it is necessary to preliminarily detect the interference strain occurring in the direction different from the direction in which the external force is applied actually to the airplane model and to calibrate a measurement result obtained in the wind tunnel experiment. For this purpose, i.e., to measure the relationship between the actual external force and the interference strain, a wind tunnel balance calibrator is used.
For example, Patent Literature 1 discloses a wind tunnel balance calibrator. According to this wind tunnel balance calibrator, the wind tunnel balance is inserted into a calibration body, and a number of load jacks are coupled to the calibration body so as to surround the calibration body. The calibration body is supported on frames surrounding the calibration body via a sting. A number of restoration jacks are coupled to the frames. In addition, to couple the load jacks externally placed outside the frames and the calibration body placed inside the frames to each other, the frames are provided with through-holes through which wires for coupling them together are inserted.
In the wind tunnel balance calibrator disclosed in Patent Literature 1, when the load jacks are actuated, a load (calibration load) is applied to the wind tunnel balance with six degrees of freedom via the calibration body. In this case, since the wind tunnel balance (or calibration body) itself strains, a relative attitude (position) between a load vector and the calibration body is displaced in the vicinity of an action point (application point). By actuating the restoration jacks, the attitude is restored. In this way, by maintaining the relative attitude (position) between the load vector and the calibration body with predetermined accuracy, it is possible to apply a desired calibration load correctly to the wind tunnel balance. By measuring a strain (including interference strain) generated in the wind tunnel balance under this condition, it is possible to correctly measure the relationship between the load and the interference strain.
In general, a method of measuring the strain while restoring the attitude displacement of the calibration body caused by application of the calibration load is referred to as a repositioning method, and is one of methods for use as the wind tunnel balance calibrator.